I finally got around to making some acoustic iPhone amplifiers. When I posted my how to video on making them, I got a lot of people in the comments wanting to buy one. Check out my Etsy shop if you are interested in buying one. Also, if you want me to make you a custom one, send me an email: email@example.com and I will see what I can do.
Here is the video on how I made them and a sound test: